A micromechanical component of this type is described in German Patent Application No. DE 100 12 960.
Although applicable to any micromechanical components and structures, in particular sensors and actuators, the present invention and the problem on which it is based are explained with reference to a micromechanical acceleration sensor producible using the technology of silicon surface micromechanics (SMM).
Acceleration sensors, and in particular micromechanical acceleration sensors using the technology of surface or bulk micromechanics, are gaining increasingly large market shares in the motor vehicle equipment sector and, to an increasing extent, are replacing the hitherto usual piezoelectric acceleration sensors.
The conventional micromechanical acceleration sensors usually function in such a way that the resiliently mounted seismic mass device, which can be deflected in at least one direction by an external acceleration, brings about, upon deflection, a capacitance change in a differential capacitor device connected thereto, that change being a measure of the acceleration. A differential capacitor device having a comb structure, parallel to the surface of the substrate, made up of moving and fixed electrodes is described in the above-identified German patent application. The deflection can also be detected on the basis of a different suitable measurement method.
The sensitivity of such conventional micromechanical acceleration sensors for the measured variable (acceleration) can, at present, be adjusted substantially only by way of the rigidity of the spring mounting of the seismic mass, i.e., by way of its spring constant that must be selected beforehand. A high sensitivity in this context means, however, that the linear return forces of the springs are small, so that because of its correspondingly low load capacity, the component is usable only as a low-G sensor. For acceleration sensors that are to be used in a range with a higher maximum acceleration, for example 50 G (G=acceleration of Earth's gravity) or 100 G, the spring device must therefore be designed from the outset with a higher rigidity (spring constant).
Because of the linear correlation between acceleration and deflection, however, with a “hard” spring of this kind a large acceleration corresponds to a small deflection, and therefore also to a lower sensitivity of the acceleration sensor. For practical application, a demand exists for sensors that simultaneously exhibit a high resolution in the lower measurement range and a large measurement range, i.e., one extending up to large maximum accelerations; until now, however, the user has had either to decide on a specific range category or sensitivity category or—as a complex alternative—to use several sensors of different range categories simultaneously.
The need to select G-range categories beforehand also creates the manufacturing-related disadvantage that different layouts are necessary for each different G-range category. The aforementioned German patent application therefore proposes an acceleration sensor of the kind in which the spring rigidity is still externally adjustable even after manufacture (upon initial or final measurement), so that a single layout or design can be used for a wide range of rigidities. For that purpose, parts of the spring device are embodied in unlockable and lockable fashion, so that a desired effective spring constant can be set, in particular, by the action of a measurement current or an externally controllable magnetic field on a separation region. Once adjustments have been made they can, at most, be modified by way of another external adjustment procedure.